1. Field of the Invention:
This invention relates to a constant-speed regulating device for a vehicle which causes the vehicle to automatically run at a constant speed when driving on expressways, etc.
2. Description of the Prior Art:
In recent years, electric motor-equipped constant-speed regulating devices comprising an electric motor-driven actuator have been commonly used as constant-speed regulating devices for vehicles, due to the trend toward higher r.p.m. engines and their ease of handling in assembly.
With reference to FIGS. 4 to 6, a conventional motor-equipped constant-speed regulating device will be described. FIG. 4 is a block diagram of a conventional motor-equipped constant-speed regulating device. The constant-speed regulating device shown in FIG. 4 comprises a control circuit 1, a drive circuit 2, an actuator 3, a throttle cable 4, a throttle valve 5, and a throttle position sensor 6. The control circuit 1 receives a vehicle velocity signal input 1a, operation switch inputs 1b which designate settings, acceleration, deceleration, etc., a cancel input 1c which indicates the cancel of the constant-speed running when the brake pedal or the like is operated. The actuator 3 comprises a DC motor 3a, a reduction gear and clutch assembly 3b, and a pulley 3c. The cable 4 interconnects the pulley 3c and the throttle valve 5. The resistance of the sensor 6 varies in accordance with the degree of the opening (throttling) of the throttle valve 5.
The operation of the constant-speed regulating device of FIG. 4 in which the control circuit 1 is set to the operating condition will be described. First, the vehicle velocity signal 1a is input to the control circuit 1, and measured in the vehicle velocity measuring block 7 shown in FIG. 5, to be set as the vehicle velocity V. Then, the difference .DELTA.V between the vehicle velocity V and the target vehicle velocity is calculated in block 8. Block 9 judges whether this .DELTA.V is zero or whether the absolute value .vertline..DELTA.V.vertline. of the velocity difference .DELTA.V is smaller than a previously fixed value A. If true, no operation command is sent to the drive circuit 2, and the sequence returns to block 7. If false, block 10 then judges whether .DELTA.V is larger than another previously fixed value B which is greater than the above-mentioned value A. If false, block 11 then calculates the integral of .DELTA.V. If true and after block 11, block 12 calculates the differential of the vehicle velocity V.
Next, in block 13, the multiplications of the velocity difference .DELTA.V and a first coefficient K.sub.1, the integral of the velocity difference .DELTA.V and a second coefficient K.sub.2, and the differential of the velocity difference .DELTA.V and a third coefficient K.sub.3 are added together, and the result is designated as E as follows: ##EQU1## In block 14, a motor voltage (or motor current) corresponding to the value E is determined and is output to the drive circuit 2. This causes the motor 3a to rotate clockwise or counter clockwise according to the value of E. After being reduced by the gear and clutch assembly 3b, the rotation of the motor 3a causes the pulley 3c to rotate, thereby actuating the throttle valve 5 through the cable 4 so that the throttling is adjusted.
The engine characteristics, as shown in FIG. 6 in which the horizontal axis is the vehicle velocity and the vertical axis the thrust, can be indicated by curves 15a to 15e using the degree of throttling as a parameter. If all external conditions of the vehicle are the same, the running resistance of the vehicle, as indicated by the broken line 16, can be expected to be a function of the vehicle velocity. The engine output and running resistance of a vehicle running at velocity V.sub.1 and degree of throttling 15c exist at point 17. Assuming that the running resistance changes from point 17 to point 18 due to changes in road conditions, etc., and the degree of throttling remains in the curve 15c, the operating point will change to point 19 and the velocity will change from V.sub.1 toward V.sub.2. Therefore, in order to maintain the same vehicle velocity V.sub.1, the degree of throttling must be changed from 15c to 15d. This operation of the throttle valve 5 is achieved by the rotation of the pulley 3c.
In the above configuration, however, the amount of rotation of the pulley 3c i.e., the throttling of the throttle valve 5 must be based on the engine characteristics and running resistance characteristics (i.e., gear positions, vehicle characteristics), etc. Therefore, it is necessary to finely adjust the above-mentioned constants K.sub.1, K.sub.2 and K.sub.3 for each vehicle. Further, adjustment of the condition of the mechanical linkage from the gear and clutch assembly 3b through the pulley 3c and the cable 4 to the throttle valve 5 is also necessary for each vehicle.
This necessitates the control circuit 1 to be separately adjusted for each type of vehicle, so that the common application of a constant-speed regulating device to different types of vehicles is difficult or impossible.
The DC motor 3a rotates at an angular velocity .omega. determined by the following equation (2): EQU T.sub.m -T.sub.L =J.sub.m .multidot.(d.omega./dt)+D.sub.m .multidot..omega.(Eq. 2).
where T.sub.m is the motor torque, J.sub.m the motor shaft reduced inertia, T.sub.L the load, and D.sub.m the viscous drag. The above-mentioned determination of the motor voltage (or current) in block 14 causes only the motor torque T.sub.m to be determined, but the motor speed .omega. remains to be determined. The angular velocity .omega. is determined by equation (2). The load T.sub.L, in particular, in equation (2) varies with the vehicle, and the motor speed is affected by this.
Since the degree of the throttling of the throttle valve 5 is equal to the integral of the angular velocity .omega., the degree of the throttling is not determined by merely determining the motor voltage (or current), resulting in that the degree of the throttling must be fedback via the throttle position sensor 6 to correctly determine the degree of throttling.